Evolution of the Montana de Oro Bluff

©Bob Field 2005

The rugged beauty of the evolving coast reveals the powers of the sea, sky, land, and life itself. Seasonal change and tides may be discussed. Rain cancels. Meet at Bluff Trailhead, 200 yards south of Visitor Center at Montana de Oro State Park. (*M) 3 mi., 3 hr.

Rubes cartoon reprinted by permission of Leigh Rubin

Leigh Rubin is a “Friend of Global Evolution” as are many people in Cal Poly’s College of Science and Mathematics and in local nature organizations. For more information or to become a friend, visit the Global Evolution Education Project.

The following is a rough draft of a brief description of a typical walk – each walk is different and the content is rapidly evolving.

At the Trailhead – The MdO Bluff is a special place because of its intrinsic beauty, the result of the meeting of sea, sky, and land. As we walk along the bluff trail, we will stop to examine graceful peaks, marine terraces, rugged bluffs, speckled and layered sedimentary rocks, powerful crashing waves, the light and color of the sky, and examples of the five kingdoms of life – plant, animal, algae, fungus, and bacteria. Everything you see from the bluff has a natural history; that is, everything changes over time.

The trail ends 1.5 miles from here. At each stop there will be time to look around and to talk about our theme. We will also pause briefly at times to look at interesting features. Because our theme is evolutionary processes, we will not be identifying every plant, bird, rock that we pass on the way out, but we can do some of that on the return walk if you like. Also, we can discuss seasonal change and tides at the end of the trail. You can also stop at Corallina Cove to look at tide pools on the way back. As we walk, be on the lookout for special things like coyotes or marine mammals, etc., but also look closely at the ordinary things you see.

Pause - Why do we cross a bridge here? Point out poison oak and reference toxins that plants can produce.

Pause – Look out over Smuggler’s Cove and discuss the forces that created and shaped it. The creek that occasionally flows under the bridge we crossed opened this area up and deposited some of the material in this area. Wave action played a major role in widening the cove. If you look across at the vertical striations, you see evidence that water flowed down the steep face of the rocks following rains.

Stop 1 – The power of the sea is revealed in the crashing waves that erode the bluffs today. Below the bluff, you can see the top layers of sedimentary rocks that are actually 2000 feet deep.

The rocks came from a mixture of the silica skeletal remains of organisms that settled to the sea floor and other fine sediments that washed to sea from the land. The organisms lived in the surface waters of shallow seas that covered this area seven million years ago. These rocks have finer grains of silica than sandstone and include the remains of the hard tests of plankton, mostly diatoms. The golden algae build tests from silica dissolved in seawater.

Notice that there are regular layers in the rock, typically a few inches. Each of these layers may have taken decades or centuries to form. Within a layer, there may be a finer structure that represents seasonal variations in sedimentation rates. The space between the layers may represent a brief rapid deposition that erodes more easily because it had less time to form and compact. Notice that the rocks form fingers. Some areas are missing because they wear faster because the original rocks were softer. We will see more examples of this later.

Horizontal depositions formed at a depth of perhaps 1000 feet below sea level and covered an area of 1000 miles or more. Older sedimentary rocks may form layers up to ten miles thick under these rocks.

Hundreds of square miles of these rocks were uplifted, folded, and then carved by wind and water as they emerged from the sea. Notice that the rocks are tilted so as to face toward the south, the direction we are walking. Which rocks are older, the ones on the left or on the right as we look down from the bluff?

Valencia Peak was also uplifted from the sea floor by seismic forces between the North American and Pacific tectonic plates. The lighter sedimentary rocks were driven over the continental shelf as the heavier iron-rich ocean crust sank below the continental margin. Waves also carved the marine terraces of Valencia Peak during lulls in the uplift.

The energy for the uplift is geothermal: heat escapes from the Earth’s interior by convection of molten rock, the same force that lifts continents above the sea floor. Even the silica in the ocean that formed the plankton came from less dense molten rocks deep in the Earth that slowly “floated” to the Earth’s surface. Morro Rock is a volcanic plug that formed about 26 million years ago hundreds of miles south of here.

The conglomerate of rocks that buried the wave-cut folded rock layers is an alluvial fan that washed down from the hills after being eroded by wind and water from the uplifted sediments. Later creeks channeled the water and carved the creek beds and the coves and deposited onto the beaches and into the sea.

Stop 2 – We check the rocks to see if they are still tilted to the south. Absorption of sunlight by the oceans keeps the oceans from freezing solid because the Earth’s surface is constantly cooling as it radiates energy back into space. Sunlight is absorbed near the ocean’s surface where evaporation initiates the water cycle: evaporation, condensation, precipitation, and surface transport. The web of life is based on sunlight.

Stop 3 – Where does the sea get its power? Waves are generated by winds which are produced when the atmosphere absorbs sunlight. Temperature differences cause variations in air density which leads to air flow or wind.

Clouds and fog cool the Earth during the day by scattering sunlight into space. Clouds and fog warm the Earth at night by scattering infrared back to the Earth. Ozone absorbs ultraviolet, shielding us from its harmful rays. Greenhouse gases trap heat on the Earth’s surface. We should also look for optical phenomena in the sky and the surf.

The atmosphere used to be mostly carbon dioxide. Photosynthesis by cyanobacteria (“blue green algae”) removed carbon dioxide and released oxygen. This led to the oxygen holocaust which killed off most of the things living at the time. With the big drop in greenhouse gases, wouldn’t you expect global cooling to freeze the oceans solid? Not if the Sun has been getting brighter and hotter over time.

Check the rocks to see if they are still tilted to the south.

Stop 4 – The theme of our walk is that everything evolves.

Where did all these plants and animals come from? How did plants and algae “learn” to convert sunlight into food? How did plants and animals adapt to the land from the sea? How do bacteria influence plants? What do plants do? What are they made out of?

How do they interact with each other? How do they interact with the other four kingdoms and with the physical environment?

The natural history of the flowering plants you can see on the bluff involves the other four kingdoms: they evolved from algae with the help of bacteria for fixing nitrogen, fungi to provide phosphorus, and animals (insects or birds or bats) to pollinate. Co-evolution, cooperation, competition, and reproductive strategies are all factors in the ecosystem that you see here. Furthermore, some cyanobacteria evolved into algae and plant chloroplasts, produced atmospheric oxygen, and removed carbon dioxide, preventing another Venus.

Chance mutations of DNA imbued the descendants of green algae to evolve into multicellular, differentiated, vascular plants with the ability to form leaves and to form and disperse seeds through the production of flowers and fruits. Changing conditions favored the descendants with certain traits by means of natural selection.

So everything you see on land has ancestors that lived in the sea.

Pause - We will keep going but I point out the trail to Corallina Cove for future reference if you want to go tide pooling or examine the beach.

Stop 5 – From the bridge, you can see that the creek that flows into Corallina Cove is unusually straight. You might suspect that this feature did not occur naturally, but one plausible natural explanation is that an earthquake fault line created a straight channel for the creek’s water that helped carve the cove.

We already discussed geothermal energy and seismic movements. Where does the heat come from? Originally the Earth was molten because of the gravitational and kinetic energy of dust and rock condensing to form our planet. Radioactive decay of atoms in the mantle has released enough energy to keep the Earth’s interior from cooling enough to halt the convection process in the mantle that builds continents. Otherwise the land would erode and vanish. Without convection, volcanism would not recycle buried carbon from the sea floor to the atmosphere. Without atmospheric carbon dioxide to trap heat, the climate would change and the oceans would cool and freeze.

The Earth collects organic matter on its surface, unlike the deep blue sea, where material sinks far beyond the reach of sunlight. The solid Earth provides a sea floor, particularly valuable on the shallow continental shelf where sunlight reaches things that live on the bottom. Can plants use the nitrogen from the air? How do you think nutrient nitrogen becomes available to plants?...

Stop 6 – Check the rocks to see if they are still tilted to the south. Corallina Cove is at a syncline where the rock folds changed direction – this is the bottom of the fold. These rocks are the youngest rocks we have seen so far. So which rocks are older those to the north or south? That may have been related to a fault line and why the water ran down along a fault and formed the cove. It’s time to talk about what is in the tide pools briefly. There are creatures related to things living on the bluff. If it’s green in the tide pool, what does that tell you? The sea anemone looks like a plant and is green but it is an animal with photosynthetic microbes living in its tissues. The cove is named after the pink Corallina alga which is reminiscent of its namesake, corals, which are inanimate animals, but it is a photosynthetic alga that does not have green chlorophyll and has a stony skeleton made from calcium. The tide pools have many other creatures like the sea star, urchin, sculpin, and many creatures with shells.

Pause – The tilt of the rocks has changed again - they are facing south again – so we have found the top of the fold in the rocks - an anticline. We talked earlier about the diatoms whose hard mineral body contributed to the sedimentary rocks. Where did the organic parts go? Some was consumed or decomposed, but some may have been trapped in the sediments - so an anticline may be a good place to look for oil.

Stop 7 – This is my favorite rock (see picture on theme page). We have walked over a mile to my favorite rock in about 120 minutes. The end of this trail is about five or ten minutes away. The trailhead is less than 40 minutes away unless you visit the tide pool visit Corallina Cove on the way back. If you don’t want to continue, you can return to the trailhead in less than 30 minutes.

End of the trail - The barbed wire fence is the end of the line. Coon Creek cove often harbors a variety of large birds. Is there anything else we have time to observe or discuss?

The appearance and behavior of plants and animals vary with daily and seasonal changes in the environment including tides and weather as a result of natural selection. How do plants “know” when it is time to grow and bloom? How do birds know when to migrate or produce breeding plumage? How do other animals know when to be active or dormant? How do seasonal changes in sunlight and moisture influence plants and animals? The summer thaw in the frigid zones keeps the oceans from freezing solid.

Why do we have seasons? What causes tides? Would we have tides without the Moon? Why does the Earth rotate daily? Do tides vary seasonally? Why does the Moon rotate and revolve monthly? How do tides affect tide pool life? Who lives in tide pools? Where did Morro Rock come from? Why do continents move? Where did the continents come from? Where did the Earth, oceans, air, and Sun come from? Where did atoms like oxygen, carbon, nitrogen, silicon come from?

Everything evolves; everything changes over time - the sea, sky, land, and life itself.

It is the role of science to provide plausible natural explanations for natural phenomena. Science is just getting started, so be patient: it may take a century or more to explain everything.

How do things change? When energy flows, (local) complexity (often) grows.

Some key words to Google: coevolution, adaptive radiation, convergent evolution, symbiosis, competition, cooperation, ecosystems, kingdoms, cell complexity.

For more information about global evolution and my Global Evolution Education Project, visit my GEEP page.